1. Field of the Invention
This invention relates to a process and apparatus for removing, recovering and treating hazardous and non-hazardous components from process streams generated from a continuous system for separating organic and inorganic constituents from contaminated material. More particularly, this invention relates to a thermal desorption/recovery process designed to remove and recover constituents generated from processing a solid or sludge feed, using thermal, condensation, solvent stripping, filtration and gravity separation techniques.
2. Description of the Related Art
A need has arisen to decontaminate inert materials such as soil, sludge, biological and other waste materials contaminated with chemical compounds. In particular, it is necessary to decontaminate waste products and recover the resources contained in the waste from early manufactured gas plant (MGP) sites, for example. Also, a need has arisen to recover and treat hazardous and non-hazardous components from process streams generated as a result of manufacturing processes, especially for a process that is flexible and amenable to be used for either discarded waste or in-stream recovery for return to a manufacturing process.
Historically, at the turn of the century, in operating manufactured gas plants, coal was heated to drive off organic gases, which were used for heating and lighting. The gases were sent to very large receiver buildings, typically 100 to 200 feet across, and generally made of concrete or some other cementitious material. The gases were cooled in these receiver buildings. However, these gases contained heavy tars which were separated by cooling and gravity. These tars were separated out from the gases and would build up on the bare ground floors in the receiver buildings. Thus, one to twenty or more feet of soil would be contaminated with these tars. The surrounding ground would likewise be contaminated. This also resulted in pollution of nearby ground water. Accordingly, a need has arisen to decontaminate such soil.
In the past, such contaminated soil or material would be sent to a designated landfill. However, such disposal merely relocates the contaminated soil.
Several attempts have been made to treat such contaminated material. For example, incineration has become a generally accepted means for destroying organic contaminants in such contaminated material. Such incineration may involve collecting, packaging, and transporting a large mass of contaminated material to a licensed incineration facility, heating the large mass of inert solids to very high incineration temperatures to decompose the proportionately small amount of target contaminants and packaging and returning the materials back to the treatment site from where they were removed, or disposed of in a secure landfill. Accordingly, such incineration has drawbacks.
U.S. Pat. No. 5,086,717 (McCrossan) discusses the removal of volatile organic chemicals (VOCs) from soil contaminated with gasoline, diesel fuel and the like. The soil is heated in a burner-heated drum to substantially vaporize the VOC's. The vaporized VOC's are sent to a scrubber to be absorbed into the scrubber water, along with any airborne soil particulates. The VOC and particulate-laden water is then sent to a settling basin to remove the particulates. Particulate-free VOC-laden water is removed from the basin to an air stripper where the VOC's are vaporized. The vaporized VOC's are sent back to the drum burner.
U.S. Pat. No. 5,188,041 (Noland, et al.) discusses removing VOC's from soil and waste materials. The contaminated material is introduced to a hopper, which is sealed from the atmosphere to prevent fugitive emissions of the contaminants. The material is conveyed under sealed conditions into a heated vapor stripping conveyor to strip moisture and contaminants. Non-oxidizing gases are streamed at a controlled temperature over the material to carry the contaminants and moisture away from the material. The flow rate and temperature of the gases are maintained to prevent undue surface drying of the material as it passes through the conveyor.
U.S. Pat. No. 5,150,175 (Des Ormeaux) discusses removing and recovering constituents from a waste stream at temperatures higher than the boiling point of the constituents, and in particular, a process for the treatment of hazardous waste in an inert atmosphere. The waste is heated and moved at a specified retention time, through a heat zone. Components are separated and are released in a gaseous state, either from a liquid or a solid within the waste stream. The gaseous components are transferred through a flow of an inert medium, such as nitrogen gas, to inhibit combustion of the components or to prevent the combination of oxidation, or oxygen being used as a catalyst to form even more hazardous compounds. The gaseous components then are released in a distilled state, which is then mixed with the waste, or in emulsion with the waste stream. This patent also discusses "sweeping" the waste material contained in the heating chamber with an inert or carbon dioxide gas.
Some attempts have been made to separate contaminants from soil or sludges without incineration. For example, U.S. Pat. No. 4,977,839 (Fochtman, et al.) discusses separating chemical contaminants such as VOCs and polychlorinated biphenyls (PCB's) from soils or sludges. The contaminated materials are volatilized below incineration temperature, with continuous removal of evolved vapors, long enough to separate the contaminants. The vapors are catalytically oxidized to destroy the volatilized chemical compounds.
U.S. Pat. No. 5,103,578 (Rickard) relates to the removal of volatile organic compounds such as PCB's from soils, without incineration. The contaminated soil is introduced in batch into a vessel and heated to a temperature between 300.degree. F. to 600.degree. F., preferably in the absence of an inert gas. The vessel is subjected to a vacuum to cause the contaminant to flash to a contaminant vapor, which is condensed to a disposable liquid.
However, none of these patents teaches or suggests a process and apparatus for removing, recovering and treating hazardous and non-hazardous components from process streams generated from a continuous system for separating organic and inorganic constituents from contaminated material, as in the present invention.